The frequency of input signals provided to semiconductor integrated circuits (ICs) has steadily increased over time. As IC input signals reach the radio frequency (RF) range with frequencies of approximately a gigahertz or more, complex impedances at IC input nodes become significant. The complex impedance of an IC input node can create impedance matching issues between the source of an input signal and an input node of the IC. An impedance mismatch between the source of the input signal and the input node of the IC can result in a percentage of the power of the input signal reflecting back from the input node to the source of the input signal. The reflection of input signal power creates inefficient delivery of input signal power to the input node.
Complex impedances are a function of multiple small capacitances and inductances associated with devices coupled to the input node of the IC. These small capacitances and inductances can include gate capacitances, inductances and capacitances associated with interconnect lines, packaging bond wire inductances, capacitance associated with input pads, capacitances associated with electrostatic discharge structures, and the like. Since the small inductances and capacitances that form the complex impedance become more significant at higher frequencies, impedance mismatches tend to increase at higher frequencies. These impedance mismatches lead to a reduction in bandwidth of the input node.
To avoid signal power loss, RF systems strive to appear as a purely resistive impedance, typically 50 ohms, at each RF input and RF output. To offset complex impedances at IC input nodes, a matching network with the intended function of cancelling complex impedances can be implemented at each IC input node. One such matching network is a T-coil network. In general, a T-coil network includes two inductors electrically coupled in series with an input load electrically coupled to the T-coil network at the coupling point between the two inductors. The T-coil network can reduce or cancel the complex impedances associated with a capacitive load at the IC input node. The implementation of a T-coil network at an input node of an IC can increase the bandwidth of that input node. In addition, the T-coil network can improve RF system performance at the input node, for example, by reducing return loss, decreasing bit error rates, increasing power gain, and the like.